Digital systems can be implemented using off-the-shelf integrated circuits. However, system designers can often reduce cost, increase performance, or add capabilities by employing in the system some integrated circuits whose logic functions can be customized. Two common kinds of customizable integrated circuits in digital systems are application-specific integrated circuits (ASICs) and field-programmable gate arrays (FPGAs).
ASICs are designed and manufactured for a particular application. An ASIC includes circuits selected from a library of small logic cells. A typical ASIC also includes large special-purpose blocks that implement widely-used functions, such as a multi-kilobit random-access memory (RAM) or a microprocessor. The logic cells and special-function blocks must be placed at suitable locations on the ASIC and connected by means of wiring.
Application-specific integrated circuits (ASICs) have several advantages. As an ASIC contains only the circuits required for the application, it has a small die size. An ASIC also has low power consumption and high performance. However, ASICs have some disadvantages. It takes a lot of time and money to design ASICs because the design process is complex. Creating prototypes for an ASIC is complex as well, so prototyping also takes a lot of time and money.
Field-programmable gate arrays (FPGAs) are another kind of customizable integrated circuit that is common in digital systems. An FPGA is general-purpose device. It is meant to be configured for a particular application by the system designer.
Field-programmable gate arrays (FPGAs) have advantages over application-specific integrated circuits (ASICs). Prototyping an FPGA is a relatively fast and inexpensive process. Also, it takes less time and money to implement a design in an FPGA than to design an ASIC because the FPGA design process has fewer steps.
FPGAs have some disadvantages, the most important being die area. Logic blocks require more area than the equivalent ASIC logic cells, and the switches and configuration memory bits in routing crossbars (XBARs) require far more area than the equivalent wiring of an ASIC. FPGAs also have higher power consumption and lower performance than ASICs.